Such filters are known, e.g. from SE-A-7406315-7, which discloses a filter where the filtrate is lead into central annularly arranged axial ducts, and from SE-A-8305817-2, which discloses a filter in which the filtrate is led to ducts at the disc periphery.
In certain filtering cases, such as dewatering, i.e., when the concentration of fibers in a pulp suspension is to be increased from, e.g., 0.5% to 3%, a very large filtrate flow capacity is required in the filter used, as well as relatively high rotational rates. Conventional filters which are in themselves excellent filters in higher concentration ranges, i.e., when smaller filtrate quantities are present and lower rotational rates are utilized, are not capable of removing large amounts of filtrate in the short time available from when a disc sector rises above the suspension surface until the filter cake deposited on the sector is to be removed. As a result, the filtrate runs out of the section and again wets the dewatered filter cake.